The oligomeric enzyme tryptophan synthetase is to be characterized from the differentiating bacterium Bacillus subtilis. The specific questions to be answered are whether or not this organism contains an enzyme that is significantly different from those of the non- differentiating bacteria already studied, and if so, are there any apparent selective advantages to these differences. The first objective is therefore to continue the characterization of the alpha and beta 2 components of tryptophan synthetase as separate entities. This characterization will include a study of association- dissociation phenomena of the beta and alpha monomer/dimer through ultracentrifugation and sucrose density centrifugation, sequencing of catalytically important peptides of alpha and beta, and a study of alpha and beta immunological cross-reactivity. Secondly, the components will be characterized as their physiological complex, presumably alpha2 beta2. This will include a kinetic analysis of the primary (overall) and subsidiary reactions catalyzed by the complex, an examination of the association phenomenon as a function alpha2 beta2 binding in the ultracentrifuge and the effect of such factors as substrate and cofactor on this binding by sucrose density centrifugation, and a study of sulfhydryl modification of the individual components and its effect on binding and catalytic function. Thirdly, heterologous alpha2 beta2 complexes, as for examples between B. subtilis beta2 and E. coli alpha, will be characterized using the same techniques that described the homologous situation.